Overview of SCSI-3 Standards

Overview of SCSI-3 Standards

The SCSI-3 standard is a family of other standards, as I have mentioned. These standards are organized into a structure as defined by the SCSI-3 architecture documents, which categorize the other documents into several groups. On this page I will list, and briefly describe, the documents that make up the SCSI-3 standard family. I am not going to get into too much detail here, as most of these standards will be of only passing interest to the PC user--even one who uses SCSI hardware. :^)

Note: These documents are constantly being updated as a result of ongoing work. While current as of this writing in late 2000, every month documents are revised and change status. For the latest status, or to download drafts of any documents under development, see the T10 technical committee web site or the other web sites referenced below.

The first group are the command sets, which define commands used for various SCSI commands. These include the following:

Command Set	Description	Document	Abbreviation and Generation	Status	Standard or Project
Shared	Commands defined for all SCSI devices	SCSI-3 Primary Commands	SPC	Published	X3.301-1997
			SPC-2	Pending Publication	T10 1236-D
			SPC-3	Development	T10 1416-D
Block	Commands defined for random-access devices that transfer data in blocks, such as hard disks	SCSI-3 Block Commands	SBC	Published	NCITS.306-1998
Block		SCSI-3 Block Commands	SBC-2	Development	T10 1417-D
Block (Reduced)	A "simplified" version of the block command set	SCSI-3 Reduced Block Commands	RBC	Published	NCITS.330-2000
Stream	Commands for streaming, sequential-access devices such as tape drives	SCSI-3 Stream Commands	SSC	Published	NCITS.335-2000
Stream		SCSI-3 Stream Commands	SSC-2	Development	T10 1434-D
Medium Changer	Commands for medium-changing devices such as tape or disk "jukeboxes"	SCSI-3 Medium Changer Commands	SMC	Published	NCITS.314-1998
Medium Changer		SCSI-3 Medium Changer Commands	SMC-2	Development	T10 1383-D
Multimedia	Commands for "multimedia devices" (typically, optical drives)	SCSI-3 Multimedia Commands	MMC	Published	X3.304-1997
			MMC-2	Published	NCITS.333-2000
			MMC-3	Development	T10 1363-D
Multimedia (Reduced)	A "simplified" version of the multimedia command set	SCSI-3 Reduced Multimedia Commands	RMC	Development	T10 1364-D
Controller	Commands for RAID controllers	SCSI-3 Controller Commands	SCC	Published	X3.276-1997
Controller	Commands for RAID controllers	SCSI-3 Controller Commands	SCC-2	Published	NCITS.318-1998
Enclosure Services	Commands for SCSI device enclosures	SCSI-3 Enclosure Services	SES	Published	NCITS.305-1998
Object Based Storage Devices	Defines an object-oriented command set for accessing data	Object Based Storage Device Commands	OSD	Development	T10 1355-D

The other two groups of standards are protocols and interconnects. Protocols define how data is interchanged, and transports describe the physical ways that protocols are implemented. They are closely related and in some cases now are defined by a single document, which makes them a bit difficult to present in an organized way. I will start by discussing the various protocols (also called transports by some):

Protocol	Description	Document	Abbreviation and Generation	Status	Standard or Project
Interlocked (Parallel Bus)	Defines the protocol for "regular" parallel SCSI	SCSI-3 Interlocked Protocol	SIP	Withdrawn; now incorporated into later versions of the SCSI-3 Parallel Interface	--
Fibre Channel	Defines the protocol for running SCSI on the Fibre Channel interface	SCSI-3 Fibre Channel Protocol	FCP	Published	X3.269-1996
Fibre Channel		SCSI-3 Fibre Channel Protocol	FCP-2	Pending Publication	T10 1144-D
Serial Bus	Defines the protocol for transporting commands over the IEEE-1394 (serial) interface	Serial Bus Protocol	SBP	Withdrawn	--
Serial Bus		Serial Bus Protocol	SBP-2	Published	NCITS.325-1998
Serial Storage Architecture	Defines the transport layer for Serial Storage Architecture, an advanced interface used in servers and enterprise hardware; there are two documents that specify the protocol	Serial Storage Architecture SCSI-3 Protocol	SSA-S3P	Published	NCITS.309-1998
Serial Storage Architecture		Serial Storage Architecture Transport Layer	SSA-TL2	Published (replaced SSA-TL1)	NCITS.308-1998

Finally, this table shows the interconnect standards, also sometimes called physical layer documents (since they describe how devices are physically connected):

Interconnect	Description	Document	Abbreviation and Generation	Status	Standard or Project
Parallel Bus	Describes the electrical signaling, connectors and related issues associated with "regular" parallel SCSI; starting with SPI-2 these include the formerly separate SIP protocol document	SCSI-3 Parallel Interface	SPI	Published	X3.253-1995
			Fast-20 (addendum to SPI)	Published	X3.277-1996
			SPI-2	Published	X3.302-1999
			SPI-3	Pending Publication	T10 1302-D
			SPI-4	Development	T10 1365-D
Fibre Channel	Several documents define alternative physical layer standards for Fibre Channel; these are maintained by the T11 technical committee and include Fibre Channel Arbitrated Loop (FC-AL) and several revisions of the Fibre Channel Physical Interface (FC-PHx)
Serial Bus	The physical layer standards for the serial bus (IEEE-1394) are developed by the IEEE High Performance Serial Bus Bridges Working Group (P1394)
Serial Storage Architecture	Defines the physical connections for the Serial Storage Architecture interface	Serial Storage Architecture Physical Layer	SSA-PH	Published	X3.293-1996
Serial Storage Architecture		Serial Storage Architecture Physical Layer	SSA-PH2	Published	NCITS.307-1998

Whew. Well, you can certainly understand now why some people find SCSI-3 "a bit confusing". :^) I hope that this "road map" helps to make things a bit more clear for my readers though!

Next: SCSI(-3) Parallel Interface (SPI)

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